Abrupt steering and counter-steering maneuvers in e.g. obstacle avoidance maneuvers, when changing lanes, free style, and like maneuvers may cause instabilities of the vehicle at a high coefficient of friction. There is an increased risk of rollover for vehicles with a high center of gravity.
A great number of driving stability control systems are known in the art in order to automatically counteract these vehicle instabilities. The term ‘driving stability control’ covers five principles for influencing the driving performance of a vehicle by means of predeterminable pressures or brake forces in or at individual wheel brakes and by means of intervention into the engine management of the driving engine. These systems concern brake slip control (ABS) preventing the locking of individual wheels during a braking operation, traction slip control (TCS) preventing the spinning of the driven wheels, electronic brake force proportioning (EBP) regulating the ratio of brake forces between front axle and rear axle of the vehicle, anti rollover braking (ARB) preventing rollover of the vehicle about its longitudinal axis, as well as yaw torque control (ESP—Electronic Stability Program) ensuring stable driving conditions during yawing of the vehicle about the vertical axis.
Hence, ‘vehicle’ in this connection refers to a motor vehicle with four wheels which is equipped with a hydraulic, an electro-hydraulic, or electromechanical brake system. In the hydraulic brake system, the driver can build up brake pressure by means of a pedal-operated master cylinder, while the electro-hydraulic and electromechanical brake systems develop brake force in response to the sensed braking request of the driver. A hydraulic brake system will be referred to in the following. Each wheel has a brake with which each one inlet valve and one outlet valve is associated. The wheel brakes are in connection to the master cylinder by way of the inlet valves, while the outlet valves lead to a non-pressurized reservoir or low-pressure accumulator. There is still provision of an auxiliary pressure source that is able to develop pressure in the wheel brakes even irrespective of the position of the brake pedal. The inlet and outlet valves are electromagnetically operable for pressure control in the wheel brakes.
To detect conditions related to driving dynamics, there are four rotational speed sensors, one per wheel, a yaw rate sensor, a lateral acceleration sensor, and at least one pressure sensor for the brake pressure generated by the brake pedal. Instead of the pressure sensor, a pedal travel sensor or pedal force sensor may also be used, if the auxiliary pressure source is so arranged that it is impossible to make a distinction between brake pressure built up by the driver and pressure from the auxiliary pressure source.
In a driving stability control operation the driving behavior of a vehicle is influenced in such a manner that the driver can better master it in critical situations. A critical situation in this respect refers to an unstable driving condition during which the vehicle—in the extreme case—will not follow the specifications of the driver. Thus, in situations of this type, the function of the driving stability control involves imparting the performance desired by the driver to the vehicle within physical limits.
While the longitudinal slip of the tires on the roadway is primarily important for brake slip control, traction slip control, and electronic brake force proportioning, further quantities such as yaw velocity and sideslip angle gradient are included in yaw torque control (YTC). Rollover control systems typically evaluate quantities relating to lateral acceleration or rolling moments (DE 196 32 943 A1).
It would be desirable to generally avoid unstable driving situations, which are frequently not mastered by the driver so that critical driving situations cannot occur anyway.
German application DE 42 01 146 A1 discloses a system for predicting the performance of a motor vehicle and for a control based thereon, said system including a large number of acceleration sensors whose data is evaluated by means of complex calculations.